Tuesday, March 25, 2014

Multipurpose tank

Every temple built during the middle ages has some kind of a water body attached to it. Such a water body - the temple tank - served more than an ornamental function. It is believed that these tanks also played a crucial role in the ecosystem. Storing water was key, but the way these tanks were constructed ensured that they collected the runoff water from the catchment areas. Thus, the tanks were replenished during the monsoons and, unless it was a particularly bad year, remained full of water the year round. 

A paper published in 2008 identified 39 temple tanks within Chennai. The paper was about the results of a study on how Chennai's temple tanks could be used in the rainwater harvesting efforts that are essential for Chennai's water supplies. The paper went into details about how the runoff can be predicted; apparently there is an empirical parameter called the SCN Runoff Curve Number that can be used to predict it. Combining this information with factors such as evaporation loss and water depth in the tank, an estimate was made of the size the catchment area for an urban tank needed to be. Let us just say that it is far greater than what is available to any of the city's 39 tanks.

For all that, this tank linked to the Marundeeswarar temple appears to be quite full. With narrow streets around its perimeter, this tank has kept itself reasonably clean and charged up to take on the next dry season!

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